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https://issues.apache.org/jira/browse/CRUNCH-286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13806002#comment-13806002
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Gabriel Reid commented on CRUNCH-286:
-------------------------------------
The contract for a Combiner is that it can be run 0-n times (although in
reality I think it's always run either once or twice) and it must be
distributive, so a combiner that is doing something like adding 17 and is
expected to run exactly once would be breaking that contract anyhow.
I'm pretty sure that with CombineFns that follow this contract it should always
be safe to leave out the map-phase combine actions.
> ability to specify a different function for combiner & reducer
> --------------------------------------------------------------
>
> Key: CRUNCH-286
> URL: https://issues.apache.org/jira/browse/CRUNCH-286
> Project: Crunch
> Issue Type: New Feature
> Components: Core
> Reporter: Stefan De Smit
> Assignee: Josh Wills
> Priority: Minor
> Attachments:
> 0001-add-combineValues-method-with-2-function-arguments.patch, 0002-.patch,
> CRUNCH-286-prototype.patch
>
>
> Extend PGroupedTable with an extra combineValues function that accepts 2
> functions: 1 for combiner phase, 1 for reducer phase.
> This way, different algorithm can be applied.
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